Tractors and other vehicles used in farming operations must be operated precisely to obtain uniform rows during planting and to harvest crops efficiently. Typically tractors used for planting rows of crops are operated manually by an operator who drives the tractor along each row to be planted. The operator must be very careful in order to get uniform rows of planted crops. It is difficult for an operator of a tractor to maintain precise positioning of the tractor relative to rows which have already been planted since the operator has no reference other than the position of the row which was most recently been planted to use as a guide. In addition, it is difficult to maintain the concentration necessary to obtain straight rows, particularly since concentration often decreases with each passing hour and minute of planting.
One prior art method for controlling the travel path of a vehicle such as a tractor includes the use of a guidance control system that includes an automatic steering control feature. Guidance control systems for tractors typically incorporate a method for position determination such as use of a global positioning system. However, other position determination systems may also be used. These guidance control systems typically include a position determining system for determining position and a vehicle controller for controlling the steering of the vehicle. One method for position determination involves the use of satellites of the US Global Positioning System (GPS) to determine position. The guidance system typically also includes a vehicle controller operable in response to an operator input mechanism. In one such system, the operator positions the tractor at the beginning of a row in response to feedback on a display.
The display may indicate the position of the vehicle or indicate the direction that the operator must move in order to properly determine the appropriate starting point for a row. Once the operator is properly positioned and is ready to start planting a row, the operator engages an input device so as to activate the automatic steering control feature of the guidance control system. The automatic steering control feature of the guidance control system controls the steering of the tractor so as to maintain proper alignment of the vehicle as a row is planted.
When an automated steering control feature of a guidance control system is used, an operator is typically required to first enter into the guidance control system a set of parameters that describe the relationship between the tool and the tractor. This may include, xyz offset, row spacing of the crop and number of rows (or tool width). This allows an operator to attach different tools to a particular tractor. In practice, the set of parameters for a particular tool could be stored in a pre-defined library within the guidance control system and allows the operator to select a tool from a pre-defined, list of pre-configured tools instead of entering a complicated set of numerical parameters.
The guidance control system may be used several times during the growing season over the same rows. It may be used first to plow the ground, again to plant seeds, another time for weed removal between plant rows and finally for harvest. Ideally, each pass is aligned with the next pass with a minimum of error. However, errors do occur. Some of these errors arise because: 1) each tractor/tool combination has its own set of errors; 2) poor traction may result in reduced line accuracy; and 3) differences in equipment manufacturers may result in misalignment between tools. On a given pass, the guidance control system may provide excellent alignment with an ideal crop row as defined by a theoretical set of GPS coordinates. However, this is of little value if the row was originally installed with large errors and the result is plant destruction by the tractor tires or deficient fertilizer because the nozzle was positioned over dirt instead of over the plant row.
When an operator discovers that the tractor is not following the required path, the operator typically does not have time to enter a new offset and/or to otherwise correct the problem. Thus, when an operator discovers that the tractor is not following the required path, he has only two choices: 1) he can run on the exact pre-planned path as described in the mission and run the risk of destroying crops; or 2) he can override the guidance control system and operate the vehicle in manual steering mode.
When the operator overrides the guidance control system, all of the benefits of the guidance control system are lost. Visibility problems, basic consistency and the ability to follow complicated curved paths are suddenly reduced to the operators ability to manually steer the vehicle. Furthermore, to switch the guidance control system back to automatic, the operator must compare the current vehicle location (as determined by his driving) with the intended path and mentally asses whether the error condition that forced manual mode has gone away. This requires the operator to look at a display of some sort to determine if the actual row location is on the pre-planned track. Since the operator is busy steering the vehicle, this comparison requires substantial ability by the operator to perform multiple tasks. Additionally, the whole process is problematic because manual steering errors appear as tracking errors on the display. This makes use of the guidance control system difficult, particularly when only a small correction is required.
What is needed is a way to easily correct for errors in travel path when operating a vehicle under automatic steering control. More particularly, a way to correct travel path which will not require the operator to disengaged the automated guidance feature is needed. The present invention meets the above needs.